1. Field of the Invention
The invention relates to the technique of virtual private network, especially to the technique of L2 virtual private network (L2 VPN).
2. Background of the Invention
In the data communication network, packing and transporting L2 protocol data units (L2 PDU) by pseudo wire (PW) could provide emulation L2 service through IP/MPLS (Multiprotocol Label Switching) backbone network. The network adopting this technology can be referred to as a L2 virtual private network (L2 VPN). At present, there are two types of the L2 VPN based on providers:
One is the network providing virtual private wire service (VPWS). In the VPWS frame protocol (as further described in, PWE3 Architecture, draft-ietf-pwe3-arch-04.txt), the network model providing pseudo wire emulation edge-to-edge (PWE3) service is given. In the VPWS signaling protocol (as set forth in, Pseudo Wire Setup and Maintenance using LDP, draft-ietf-pwe3-control-protocol-06.txt), a label distribution protocol (LDP) signaling mechanism establishing and maintaining pseudo wires between the edge equipments of the backbone network (commonly referred to as provider edge, PE) is given.
The other is the network providing virtual private LAN service (VPLS), which raises a L2 address-based switching function on the basis of establishing pseudo wire between PE equipments. In the network, the establishment and maintenance of the pseudo wire could adopt two types of signaling mechanisms which are LDP and multiprotocol-extension border gateway protocol (MP-BGP), but the LDP signaling mechanism is commonly adopted, as can refer to Virtual Private LAN Services over MPLS, draft-ietf-l2vpn-vpls-ldp-03.txt.
In above-described two types of L2 VPN, the network model which establishes and maintains the pseudo wire by utilizing LDP is flat. It is necessary to establish an edge-to-edge backbone network tunnel (also referred to as packet switching network tunnel or PSN tunnel) and a direct LDP signaling session connection between PE equipments providing pseudo wires. When the network becomes very big and the pseudo wire service on the backbone network increases explosively, this full mesh tunnel and signaling connection will lead to the problem in network scalability. Additionally, when need to provide cross-domain pseudo wire service, it will be even the problem to be solved how to establish lots of cross-domain PSN tunnels and LDP session connections.